Helmet liner



FIG. 1 is a top perspective view of a helmet liner showing our new design;

FIG. 2 is a top plan view thereof;

FIG. 3 is a bottom plan view thereof;

FIG. 4 is a left side view thereof;

FIG. 5 is a right side view thereof;

FIG. 6 is a front view thereof; and,

FIG. 7 is a rear view thereof.

All broken lines form no part of the claimed design. 

The ornamental design for a helmet liner, as shown and described. 